ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology during our centenary year but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Léna de Framond is an author on ‘ Calibrated microphone array recordings reveal that a gleaning bat emits low-intensity echolocation calls even in open-space habitat’, published in JEB. Léna conducted the research described in this article while a master's student in Dr Holger R. Goerlitz's lab at the Acoustics and Functional Ecology research group, Max Planck Institute for Ornithology, Germany. She is now a scientific assistant in the lab of Henrik Brumm at Animal Communication and Urban Ecology, Max Planck Institute for Biological Intelligence, Germany, investigating acoustic interactions between animals and their environments: what ambient noise, weather and conspecifics do to their acoustic signals and how they react.
Léna de Framond
Describe your scientific journey and your current research focus
As far as I remember, I always wanted to be an ornithologist, which is why I started to study biology at university. This is where I discovered bioacoustics and how fascinating animal sounds are. My first encounter with spectrograms was during a short internship as an undergrad student, where I measured frog calls in different populations. Since then, I have never been very far from microphones. During my master's thesis, I investigated the effects of weather-induced changes in ultrasound transmission on bat echolocation. I am now studying the impact of noise pollution on vocalizing animals (mainly birds).
How would you explain the main finding of your paper to a member of the public?
Bats use echolocation to navigate and forage: their calls and the echoes tell them information about potential prey: size, type and position. But, because they use ultrasound (sounds too high for humans to hear), and such high frequencies don't travel very far, bats have to make up for that by calling very loudly. But how loud is very loud? Measuring the exact intensity of a call is very challenging, because we need to know how far exactly the bat is from the microphone. To solve this problem, we used several microphones together (a microphone array) to triangulate the bat's position. In this paper, we measured the amplitude of the echolocation calls of the brown long-eared bat, a notably faint European insect-eating species. We precisely calibrated the array to make sure that our measures were correct. We found that this species uses a low amplitude, which opens new questions on the echolocation strategies of related species. For example, the barbastelle bat is believed to use stealth echolocation to sneak up on moths. We suggest that this behaviour is not a special adaptation, but rather a constraint that they inherited from their relatives, the long-eared bats.
What are the potential implications of this finding for your field of research?
Bats' echolocation call amplitude determines how far they can ‘see’: the louder the call, the further they can detect insect prey. This is why we consider faint echolocation a disadvantage. But surrounding trees and the ground will also reflect much louder echoes, which can mask the faint echoes of small insects. Therefore, faint echolocation calls are more advantageous for bats foraging in cluttered space (in tree foliage, for example). Barbastelle bats, with their low-intensity echolocation in open space, don't fit this theory, so the ‘barbastelle bat–eared moth’ system is regarded as a textbook example for co-evolution between predators and prey: moths evolved ears to detect bats, and bats evolved faint echolocation to remain unheard by the moths. In the group of Plecotine, where barbastelle and brown long-eared bats belong, most species are foraging close to clutter, and hence don't need loud echolocation. In addition, they emit echolocation with the mouth close. It is not easy to call loudly with a closed mouth. In accordance, we show in this study that brown long-eared bats do not call loudly in open space, which suggests that they simply cannot call louder. This observation questions the evolutionary arms-race theory between barbastelles and moths. We suggest an alternative scenario in which barbastelles cannot call louder but use this limitation to specialize on hunting eared moths. This use of low-intensity echolocation to hunt eared insects might not be an isolated case, but several new findings show that bats previously regarded as diet specialists actually have a much wider diet.
The microphone array in the field, against the sky. Three microphones are located at each extremity of the metal structure, and a fourth one is in the centre. A bat is quickly flying by in the top right corner (we can see a small shadow).
Which part of this research project was the most rewarding/challenging?
The calibration of the microphone array required a lot of work and was quite challenging. I reproduced a workflow established by experts in signal processing, using different tools and software, to make sure that the measures did not depend on the software but were reliable and close to real values. This also enabled me to measure how far from real life values our measurements are. I knew that the method we use works well, but I had never found any measure of reliability on the localization and source level estimations. It was then very nice to find that the results of both localization and amplitude were so accurate and matched so well with real values!
Are there any important historical papers from your field that have been published in JEB?
Many! The two studies presenting call amplitude of brown long-eared bats in the lab (Waters and Jones’ 1995 paper ‘Echolocation call structure and intensity in five species of insectivorous bats’, doi:10.1242/jeb.198.2.475; and Jakobsen and colleagues’ 2018 paper ‘Directionality of nose-emitted echolocation calls from bats without a nose leaf (Plecotus auratus)’, doi:10.1242/jeb.171926) are published in JEB. The classic descriptions of interactions between bats and eared moths (Corcoran and Conner's 2016 paper ‘How moths escape bats: predicting outcomes of predator–prey interactions’, doi:10.1242/jeb.137638; and ter Hofstede and Ratcliffe's 2016 paper ‘Evolutionary escalation: the bat–moth arms race’, doi:10.1242/jeb.086686, for example) are also published in JEB, as are many other important foundational studies on bat echolocation call amplitude (e.g. Hackett and colleagues’ 2014 paper ‘A whispering bat that screams: bimodal switch of foraging guild from gleaning to aerial hawking in the desert long-eared bat’, doi:10.1242/jeb.100362). These studies set the scene for understanding the importance of call amplitude in the sensory ecology of bats and many of their ecological relationships with their prey or other bats.
If you had unlimited funding, what question in your research field would you most like to address?
If I had unlimited funding (and no technical difficulties) I would like to know whether and how the structure of artificial environments such as cities influences the acoustic signals and associated behaviors of animals. For example, buildings are large flat vertical surfaces that reflect sound very strongly. What if animals were able to use these surfaces to their advantage to direct their signals in a certain direction, or use them as shelters against noise pollution? For example, could the architecture of our cities influence territory distribution and geometries in birds that use songs to defend territories? Can they use big walls to reflect their songs in a particular direction? Do bats and birds use big walls and buildings to escape the noise pollution of large roads?
What changes do you think could improve the lives of early-career researchers, and what would make you want to continue in a research career?
A little more cooperation and a little less competition. Science works so much better when people of many areas of expertise join forces. There is a lot of pressure to be an expert in many fields at once, be at the top of technology and have the newest ideas to publish in top journals. Individuals rather than teams are judged on publishing performance, although few studies can happen without team work. While it is good to have role models to look up to, it makes it difficult for early career researchers to find a place.
Léna de Framond’s contact details: Animal Communication and Urban Ecology, Max Planck Institute for Biological Intelligence, 82319 Seewiesen, Germany.
E-mail: [email protected]
